This invention relates generally to air terminals for delivering conditioned air to an area or space and more particularly to a means for measuring the actual air flow through the air terminal with respect to a desired air flow, over a period of time.
The utilization of air distribution damper units to supply conditioned air from a central source thereof to offices, school rooms, and other similar spaces or areas in multi-room buildings have become increasingly prevalent. Such air distribution units are typically located in the ceiling of the rooms or areas being conditioned, or on the floor thereof adjacent the windows. The flow of conditioned air from the units is generally regulated by operation of suitable damper means controlled by a thermostat sensing the temperature of the space being conditioned. Thus as the temperature of the space deviates to a greater degree from a predetermined set point, a greater quantity of conditioned air is discharged into the space. Conversely, when the temperature in the space being conditioned approaches the set point, the quantity of conditioned air discharged into the space is reduced. Thus, the system varies the air volume to the space depending upon the deviation of the space temperature from the set point and the thermal load in the space. In U.S. Pat. No. 4,756,474 assigned to the same assignee as the present invention there is described a pneumatic controller for a duct pressure power air terminal unit having a volume controller which receives two pressure signals, whereby the controller bleeds one pressure signal so as to control the inflation of a bellows to thereby modulate the terminal unit to maintain a constant volume air flow through the unit. The controller bleeds the second pressure signal so as to maintain at least a minimum flow through the unit. Although the controller is a complicated pneumatic device requiring a rather elaborate internal mechanism and piping arrangement, it is an improvement over U.S. Pat. No. 4,120,453 which describes a three-way valve controller having two pressure regulators and a bleed type thermostat which provide four input signals to the pneumatic three-way-valve thereby providing a single pressure signal to the inflatable bellows.
The pneumatic air terminals in the above mentioned patents are powered by duct static pressure and require a continuous fill and bleed of the bladder to maintain a desired space temperature. However, there is no means to measure the total flow through the terminals. Thus, there is a clear need for an air distributing unit controller having means to ensure efficient operation of the unit while delivering the correct amount of desired air flow per period of time, and thus allowing accurate measurement of the total air flow into a space e.g. for tenant billing.